What Is Gestational Diabetes and How It’s Managed

Gestational diabetes mellitus (GDM) is a form of diabetes that develops during pregnancy in women who did not have diabetes before. The body produces insulin, but pregnancy hormones prevent the body from using it effectively—a condition called insulin resistance. This occurs in about 2 to 10 percent of pregnancies in the United States, depending on the population screened.

What Is Gestational Diabetes

Gestational diabetes differs from type 1 and type 2 diabetes because it begins during pregnancy and typically resolves after delivery. During pregnancy, the placenta produces hormones that naturally increase insulin resistance to ensure adequate glucose reaches the fetus. For most women, the pancreas compensates by producing more insulin. In those with gestational diabetes, the pancreas cannot produce enough insulin to overcome this resistance, resulting in elevated blood sugar levels.

Women with gestational diabetes have higher blood glucose levels than normal but lower than those diagnosed with type 2 diabetes outside of pregnancy. The condition affects the mother’s metabolism during pregnancy but does not mean she had diabetes before conception or will necessarily have it after delivery.

Risk Factors, Screening, and Diagnosis

Who Is at Risk

Certain characteristics increase the likelihood of developing gestational diabetes:

• Age 25 or older at pregnancy
• Family history of type 2 diabetes
• Body mass index (BMI) of 25 or higher before pregnancy
• Previous gestational diabetes in an earlier pregnancy
• Previous delivery of a baby weighing more than 9 pounds
• Polycystic ovary syndrome (PCOS)
• Ethnicity: higher rates among Hispanic, Black, Native American, Pacific Islander, and South Asian populations

Women with one or more risk factors do not automatically develop gestational diabetes, but screening becomes especially important.

When and How Screening Happens

The American College of Obstetricians and Gynecologists (ACOG) recommends screening between 24 and 28 weeks of gestation for most pregnant women. Women with multiple risk factors or symptoms may be screened earlier. Early screening at the first prenatal visit may occur for those with a prior diagnosis of gestational diabetes.

The glucose tolerance test (GTT) is the standard screening method. The initial screening uses a 50-gram glucose challenge test: the woman drinks a glucose solution and blood is drawn one hour later, without fasting. Results of 140 mg/dL or higher trigger a follow-up test.

The confirmatory test is the three-hour, 100-gram oral glucose tolerance test (OGTT), which requires fasting overnight. Blood is drawn fasting, then the woman consumes 100 grams of glucose, with additional blood draws at one, two, and three hours. A diagnosis of gestational diabetes requires two of four values to exceed normal thresholds: fasting 95 mg/dL, one-hour 180 mg/dL, two-hour 155 mg/dL, or three-hour 140 mg/dL.

Some practices use the one-step approach with a two-hour, 75-gram OGTT, which requires fasting and eliminates the initial screen.

Understanding Test Results

Results between normal and diabetic ranges do not indicate gestational diabetes but may prompt closer monitoring. A positive screen does not mean a diagnosis; approximately 80 percent of women who fail the initial screening test have normal results on the confirmatory OGTT.

Dietary Management

Medical nutritional therapy is the first-line treatment for gestational diabetes. A registered dietitian specializing in gestational diabetes can design a meal plan tailored to individual needs and food preferences.

The general approach emphasizes balanced meals with controlled carbohydrate portions, adequate protein, and healthy fats. A typical distribution includes 40 to 45 percent of calories from carbohydrates, 20 to 25 percent from protein, and 30 to 35 percent from fat. Carbohydrates should come from whole grains, legumes, vegetables, and fruits rather than refined or sugary foods.

Portion control matters more than restriction. For example, a breakfast might include one slice of whole wheat toast with peanut butter and a small apple rather than skipping breakfast or eating only protein. Spacing meals and snacks every two to three hours helps maintain steady blood sugar levels.

Foods to prioritize include non-starchy vegetables, lean proteins (poultry, fish, lean beef), whole grains (oatmeal, brown rice, quinoa), and healthy fats (avocados, nuts, olive oil). Foods to limit include white bread, sugary cereals, fruit juice, desserts, and regular soda. The cost of buying fresh produce and lean proteins ranges from approximately $80 to $150 per week for a family, though frozen vegetables and legumes offer budget-friendly alternatives.

Exercise and Physical Activity

Regular moderate-intensity physical activity improves insulin sensitivity and helps maintain healthy blood sugar levels. ACOG recommends at least 150 minutes of moderate-intensity aerobic activity per week for pregnant women without contraindications.

Walking is accessible for most pregnant women and requires no equipment. Swimming and water aerobics reduce joint stress from pregnancy weight gain. Stationary cycling and modified strength training with lighter weights are also appropriate. Exercise intensity should allow conversation—a woman should be able to speak but not sing during the activity.

Women should avoid starting new high-intensity exercise during pregnancy; instead, they should continue pre-pregnancy exercise routines at a modified intensity. Exercising shortly after meals can help prevent post-meal blood sugar spikes.

Monitoring and Medication

Home blood glucose monitoring allows women to track their individual response to foods and activities. Most women with gestational diabetes monitor blood sugar four times daily: fasting (before breakfast) and two hours after each of the three main meals.

Home glucose monitors use test strips and small lancets to obtain a blood sample from the fingertip. Monitors cost approximately $30 to $50, with test strips ranging from $0.50 to $1.50 each. Some insurance plans cover the cost entirely or partially.

Target ranges recommended by ACOG are fasting glucose below 95 mg/dL and two-hour post-meal glucose below 120 mg/dL, though individual targets may vary. Keeping a log of readings, meals, physical activity, and stress helps identify patterns and informs adjustments to diet and exercise.

If dietary changes and exercise do not achieve target blood sugar levels after two weeks, medication becomes necessary. Insulin is the first-line medication because it does not cross the placenta and has decades of safety data in pregnancy.

Insulin is administered via injection, typically at mealtimes and bedtime. Starting doses range from 0.3 to 1 unit per kilogram of body weight daily, adjusted based on monitoring results. Some women require basal insulin only, while others need both basal and mealtime insulin.

Metformin, an oral medication, may be offered as an alternative to insulin in some cases, though insulin remains the standard. Glyburide, another oral medication, is used less frequently due to higher rates of neonatal hypoglycemia.

Effects on Pregnancy and Baby

Untreated or poorly controlled gestational diabetes increases risks for both mother and baby. Maternal risks include preeclampsia (high blood pressure with protein in urine), increased likelihood of cesarean delivery, and type 2 diabetes after pregnancy.

High maternal blood sugar passes to the fetus, causing the fetus to produce extra insulin. Excess insulin promotes fat storage, resulting in larger-than-average babies (macrosomia). Babies weighing more than 9 pounds at delivery face increased risk of shoulder dystocia (shoulder getting stuck during delivery), nerve injuries, and birth fractures.

After delivery, babies of mothers with gestational diabetes may experience low blood sugar (hypoglycemia) because their insulin production remains elevated after the maternal glucose source is removed. Neonatal intensive care monitoring addresses this within the first 24 hours after birth.

Well-controlled gestational diabetes substantially reduces these risks. Babies born to mothers who managed their blood sugar within target ranges have outcomes comparable to babies born to non-diabetic mothers.

Postpartum Follow-Up and Future Prevention

Blood sugar typically normalizes within days after delivery, and gestational diabetes resolves in the vast majority of women. However, gestational diabetes increases the risk of developing type 2 diabetes later in life: approximately 50 percent of women with gestational diabetes develop type 2 diabetes within 15 years.

ACOG recommends a glucose tolerance test six to twelve weeks postpartum to confirm resolution. Women with a history of gestational diabetes should have periodic screening for type 2 diabetes, with repeat testing every three years.

Lifestyle measures reduce the risk of progression to type 2 diabetes. Weight management, regular physical activity, and a diet emphasizing whole grains, vegetables, and lean proteins significantly lower future diabetes risk. The Diabetes Prevention Program, a large clinical trial, demonstrated that weight loss of 5 to 7 percent combined with 150 minutes of activity per week reduced type 2 diabetes risk by 58 percent in high-risk individuals.

Breastfeeding also offers protection: women who breastfeed have a lower risk of developing type 2 diabetes compared to those who do not, even after accounting for other factors. This benefit increases with longer breastfeeding duration.